Electrostatic photography



June 30, 19159 E. c. GlAlMo, JR 2,892,445

ELECTROSTATIC PHOTOGRAPHY Filed Aug. l, 1955 2 Sheets-Sheet l INI/ElyToR.

BY m

ATTORNEY."

June 30, 1959 E. c. GlAiMo, .1R 2,892,445

ELECTROSTATIC PHOTOGRAPHY Filed Aug. l, 1955 2 Sheets-Sheet 2 AHWEMEY United States Patent vO ELECTROSTATIC PHOTOGRAPHY Edward C. Giaimo, Jr., Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Application August 1, 1955, Serial No. 525,656

6 Claims. (Cl. 118-637) This invention relates to electrostatic photography, and more particularly to means for developing electrostatic latent images.

In the art of electrostatic printing, means have been provided for causing an electrostatic charge image on a chargeable record member to be made visible. Such means include apparatus for depositing electroscopic powder on the surface of the record member. The powder adheres to those areas of the surface of the record member which carry electrostatic charges of a polarity opposite from that of the electroscopic powder.

It is an object of the present invention to provide improved apparatus for effecting the deposition of electroscopic powder onto the charged surface of a record member, which apparatus may be operated at relatively high speeds.

It is a further object of this invention to provide improved magnetic brush depositing means which is caused to traverse a record member laterally.

In accomplishing these and other objects, there has been provided, in accordance with the present invention, an improved developing apparatus wherein a plurality of magnetic elements are positioned about the periphery of a rotatable member. The magnetic elements are adapted to pick up, carry, and, after traversing the record member, drop brush-like tufts of a mixture of magnetic particles and electroscopic developer powder. After the brush-like tufts are dropped, new brushes are formed with fresh developer powder which has been added to the mixture. The rotatable member is positioned to rotate about an axis which is perpendicular to the plane ofthe record member being traversed.

A better understanding of this invention may had from the following detailed description, when read in connection with the accompanying drawings in which:

Fig. 1 is a plan view of one form of apparatus embodying the present invention;

Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1 and viewed in the direction of the arrows;

Fig. 3 is a cross-sectional view taken along the line 3--3 of Fig. l and viewed in the direction of the arrows;

Fig. 4 is a plan view of a different form of apparatus embodying the present invention; and

Fig. 5 is a cross-sectional view taken along the line 5-5 of Fig. 4 and viewed in the direction of the arrows. Y Referring, now, to the drawings in more detail, there is shown, in Figs. l to 3, a developing apparatus 2 which includes a pair of counter-rotating magnetic structures 4 and 6. The two magnetic structures are arranged for rotation about a common axis, one structure 4 operating in a path which lies within the path defined by the other magnetic structure 6. The magnetic structure 4 comprises a plurailty of magnetic members 8, which may be either permanent magnets or magnetic pole pieces which may be polarized by external magnets. The magnetic members 8 are positioned about the periphery of a rotatable support member 10, such as a disk of nonmagnetic material. The magnetic members 3 are spaced from each other and may have nonrnagnetic separators i2 therebetween.

The outer magnetic structure 6 similarly comprises a plurality of magnetic members 14 positioned about the periphery of a second rotatable support member 16 of nonmagnetic material. The magnetic members 1li are spaced from each other and may be separated by nonmagnetic separators 18.

In both of the magnetic structures 4 and 6, the magnetic members 8 and 14, respectively, are positioned perpendicular to the plane of the associated support member and parallel to the axis cf rotation thereof. Additionally, in both of the magnetic structures i and 6, the magnetic members extend downwardly from the associated support members and terminate in a common plane.

Supported above, and closely spaced from the upper ends of the magnetic members 8 and i4 by a pair of brackets 19, there is a bridging ring 213 of magnetic material. This ring 2t) provides a relatively low reluctance magnetic path for magnetic ilux owing between the upper ends of the magnetic members 3 and 14. The magnetic members S are preferably oriented with a polarity which is oppositely directed from the magnetic members 14. Thus, if the members 8 are positioned with their magnetic north pole at the tcp, the members 14 would be positioned with their magnetic south pole at the top. In this manner, there will be a magnetic field and, therefore, a fiux through the ring Z9 from one of the magnetic structures to the other.

Below the plane defined by the lower ends of the magnetic members 8 and 14, there is positioned a second or lower bridging ring 22. This lower ring 22 provides a relatively low reluctance Eux path for magnetic flux flowing between the lower ends of the magnetic members 8 and 14. Between the lower ends of the magnetic members 8 and 14 and the upper surface of the ring 22, there is positioned a guide plate 24. This guide plate 24 is preferably made of nonmagnetic material and may be relatively thin. The guide plate 24 serves as a guide member and operating bed for a sheet member 26 which is fed into operating relation with the apparatus 2. A slot 28 with a rolled or rounded edge 3) is provided in the plate 24 through which the sheet member 26 may be removed from the apparatus 2 after it has been operated upon. The sheet member 26 is a record member bearing a latent electrostatic charge image.

The inner magnetic structure 4 is coupled, through its support member 10, to a shaft 32 which, in turn, carries a driving member such as a spur gear 34 on its upper end. Similarly, the outer magnetic structure 6 is coupled, through its support member 16, to a hollow shaft 36 which surrounds the shaft 32 coupled to the inner magnetic structure. The hollow shaft 36 carries a spur gear 38. These spur gears 34 and 3S are coupled to suitable driving means (not shown) for driving the two magnetic structures about a common axis but in opposite directions.

The lower ends or" the magnetic members and 14 carry groups of brush-like tufts 49 of a mixture of magnetic particles, such as comminuted iron, and electroscopic developer powder. As the sheet member 26 is advanced past the rotating magnetic structures 4 and 6, the brush-like tufts pass in brushing contact with the surface of the sheet 26. Where electrostatic charges, of proper polarity, are present on the sheet, electroscopic developer powder from the brush-like tufts will he deposited on the sheet in the pattern of those charges. Since the two magnetic structures i and 6 rotate in opposite directions, the brushing action is from left-to-right in one case and right-to-left inthe other, as viewedin Fig. l. This arrangment tends to produce a highly uniform application of powder to the charged areas of the sheet 26.

It is apparent that, as the depositing process continues and electroscopic powder is deposited from the brushlike tufts 40, the powder would, before long, be depleted. However, in order to overcome the depletion problem, means are provided for dropping the tufts, remixing the comminuted iron with a replenished supply of developer powder, and reforming the blush-like tufts. This operation is accomplished by providing, first, a gap 42 in the upper bridging ring 20 and a similar gap 44 in the lower ring 22. This provides a higher reluctance path for the magnetic flux flowing between the two magnetic structures, thus weakening, in effect, the magnetic field which supports the tufts. Second, there is provided, in the gap in the upper ring 20, a magnetic member 46 which is poled to oppose the magnetic field set up by the magnetic members 8 and 14. This causes a further weakening of the tuft supporting field. In the presence of such a weakened field, the tufts are dropped onto a small revolving tray 48. The tray 48 is mounted on a shaft 50 and is rotated by suitable driving means (not shown). The tray 48 carries an abundant supply of the developer powder. As the tufts are dropped on the tray, the comminuted iron is mixed with the fresh supply of the developer powder which clings, through riboelectric action, to the iron particles. The trayA 43 carries the mixture out of the area of the'neutrali'zed magnetic field at the gaps 42, 44 and into the respective areas A and B where the field is re-established. At the areas A and B, the iron particles are again attracted to the ends of the magnetic members 8 and 14, and new brush-like tufts are formed, ready to be swept across the sheet member 26.

A similar but simpler apparatus embodying the present invention is shown in Figs. 4 and 5. In that apparatus, a single pass is made across the sheet member by the depositing means. An upper annulus 52 of magnetic material is supported by a plurality of polarizing magnets 54. The magnets are, in turn, secured to a mounting ring 56. The lower edge of the mounting ring 56 is provided with a suitable groove 58 to constitute a ball race for a plurality of ball bearings 60. The ball bearings 60 roll in a lower race 62 in the upper edge of a supporting ring 64. The supporting ring 64 is stationary and mounted on a base member 66. The supporting ring is made of magnetic material and is magnetically coupled to a lower annulus 68 of magnetic material by a fiat ring 70. The lower annulus 68 is of substantially the same diameter as the annulus 52. With this arrangement, a magnetic flux pathis established from the magnets 54, through the mounting ring 56, the supporting ring 64, the flat ring 70, the lower annulus 68, across a small gap to the upper annulus 52, and back to the magnets 54. Y

A ring gear 72 is mounted on the upper edge of the mounting ring 56. A suitable mating gear 74 is coupled to the ring gear 72 to drive the ring gear about its axis. The rotation of the ring gear carries the mounting ring 56, the magnets 54, and the upper annulus 52 in a corresponding rotational motion about theaxis of the gear 72. The mounting ring 56 rolls freely on the bearings 60. A retainer ring 76 is secured to the supporting ring 64 and extends above the upper edge of that supporting ring to embrace the lower edge of the mounting ring 56 so as to retain the mountingring in proper position on the supporting ring.

The supporting ring 64 is provided with a horizontal slot 78 through which a sheet member St) may be admitted to the apparatus. As before, the sheet member is a record member having a latent electrostatic charge image thereon. As the sheet member 80 enters the slot 78, it rests upon a plate 82 which supports and guides the sheetmember while it is being operated upon. The plate S2 is preferably made of a nonmagnetic material and has a transverse slot 84 through which the sheet member 80 may be fed out of the apparatus.

The lower edge of the upper annulus 52 constitutes a magnetic pole piece which carries brush-like tufts 86 of the mixture of comminuted iron and electroscopic developer powder. As the sheet member 80, with its latent charge images, is fed into the apparatus, the rotation of the upper annulus 52 carries the brush-like tufts 86 in an arcuate sweep across the'charged surface of the sheet member. Electroscopic developer powder is deposited from the tufts 86 onto the surface of the sheet member 80 in theV pattern of the charges thereon.

As in the hereinbefore described apparatus, means are provided for dropping and reforming the brush-like tufts with a fresh supply of developer powder. To reduce the field strength of the magnetic pole piece or annulus 52, a'nonmagneticrinsert or block 88 is positioned in the supporting ring 64. A similar block 90 may be placed in the lower annulus 68. These blocks may be made of brass, for example. With the effective reduction of the field strength' of the pole'piece, the brush-like tufts are dropped onto a revolving tray 92 which is mounted on a shaft 94 for rotation about the axis of the shaft. As before, the tray 92 carries an abundant supply of developer with which the dropped particles are mixed. The revolving'tray 92 carries Vthe mixture to a position where the magnetic field between the upper annulus and lower annulus isfre-established. In this position, the tufts are again formed on the lower edge of the upper annulus ready to be swept across the surface of the sheet members.

In both instances of apparatus described herein, the nature of the brushing action and the configuration of the apparatus, which permits the image on the sheet member to be developed by sweeping the surface with a generally transverse arcuate path, contribute to the provision of means whereby the latent image on a chargeable record member may be rapidly and conveniently developed. Y

What is claimed is:

1. Apparatus for developing latent charge images on an electrostatically chargeable record member, said apparatus comprising means for guiding said record member in a predetermined plane, means for establishing a magnetic field to support a first group of brushlike tufts of a mixture of magnetic particles and electroscopic powder and a second group of tufts of said mixture, means for moving said first group of tufts in a circular path across said plane in one direction about an axis perpendicular to said plane, and means for moving said second group of tufts in a circular path across said plane spaced from said first-mentioned path and being concentric with said first mentioned path in the direction about said axis opposite from the direction of the movement of said rst group of tufts, both of said groups of tufts being carried in position to brush the surface of said record member whereby to deposit said electroscopic powder on said record member in the pattern of said charge images. Y

2. The invention as set forth in claim l characterized by the addition of means forreplenishing the supply of said electroscopic powder in said tufts in both of said paths, said means including a rotatable tray for carrying a supply of said electroscopic powder, and means for reducing said magnetic field whereby to drop said magnetic particles onto said tray, said tray'being operable to return said particles and said powder to the influence of said magnetic field'establishing means to reform said tufts.

3. Apparatus for developing latent charge images on an electrostatically chargeable'record member, said apparatus comprising va nonmagnetic Yplate member for guiding said record member in a predetermined plane,

means for establishing a magnetic field to support brushlike tufts of a mixture of magnetic particles and electroscopic developing powder, means for moving said tufts in a circular path across said plane and about an axis perpendicular to said plane, said tufts being carried in position to brush the surface of said record member whereby to deposit said electroscopic powder on said record member in the pattern of said charge images, means for replenishing the supply of said electroscopic powder in said tufts, said last mentioned means including a rotatable tray for carrying a supply of said electroscopic powder, means for reducing said magnetic field to cause said particles to be dropped onto said tray, said tray being operable to return said particles and said powder to the influence of said magnetic field establishing means to reform said tufts, said tray being mounted for rotation in the plane defined by said plate, and said plate having a notch in its periphery to admit said tray.

4. The invention as set forth in claim 3 wherein said plate is provided with a transverse slot, said record member being supplied to said apparatus in said plane from the exterior of said circular path and removed from said apparatus through said slot in said plate member.

5. Apparatus for developing a latent charge image on an electrostatically chargeable record member, said apparatus comprising means for guiding said record member along a predetermined path, circular rigid magnetic means for supporting and moving brush-like tufts of a mixture of electroscopic developer powder and comminuted magnetic material in an arcuate path transverse to the path of said record member, said guide means comprising means whereby said predetermined path of said record member comprises a rst portion substantially parallel to the plane defined by said arcuate path, said guide means comprising means whereby said predetermined path comprises a second portion extending transversely to and away from the plane defined by said arcuate path whereby said tufts brush across the surface of said charged record member in one direction only, and said tufts being carried in position to brush the surface of said charged record member traversing said rst portion of said path to deposit said electroscopic developer powder on said record member in the pattern of said charge image.

6. Apparatus for developing a latent charge image on an electrostatically chargeable record member, said apparatus comprising means for guiding said record member along a predetermined path, circular rigid magnetic means for supporting and moving brush-like tufts of a mixture of electroscopic developer powder and comminuted magnetic material in an arcuate path transverse to the path 0f said record member, said guide means comprising means whereby said predetermined path of said record member comprises a rst portion substantially parallel to the plane defined by said arcuate path, said guide means comprising means whereby said predetermined path comprises a second portion extending transversely to and away from the plane defined by said arcuate path whereby said tufts brush across the surface of said charged record member in one direction only, said tufts being carried in position to brush the surface of said charged record member traversing said first portion of said path to deposit said electroscopic powder on said record member in the pattern of said charge image, means for replenishing the supply of said electroscopic powder in said brushing tufts, and said last named means being located beneath the plane of said arcuate path of said tufts over said record member and to one side thereof.

References Cited in the le of this patent UNTTED STATES PATENTS 2,254,531 Kirchner et al. Sept. 2, 1941 2,276,328 Melton et al. Mar. 17, 1942 2,573,952 Bretherton Nov. 6, 1951 2,645,529 Jenner July 14, 1953 2,786,441 Young Mar. 26, 1957 OTHER REFERENCES Berry et al.: "Ferromagnetography-High-Speed, General Electric Review, July 1952, pages 20, 21, and 22 and 61.

Young et al.: Electrofax, Reprint from R.C.A. Review, December 1954, vol. XV, No. 4, pages 471, 472, 480, and 481. 

